The present invention relates to an apparatus for converting mainly waste synthetic resin into oil by heating the synthetic resin in a heating vessel.
By heating thermoplastic synthetic rein to be liquified, then gasifying the liquid synthetic resin to gas, then cooling the gaseous synthetic resin, the thermoplastic synthetic resin can be converted into oil. To carry out this process, apparatus for converting synthetic resin into oil by heating the resin have been developed.
For example, in Japanese Patent Publication No. 17879/ 1986, an apparatus for converting synthetic resin into oil having a heating vessel on a screw conveyor is disclosed.
In the apparatus having a heating vessel, waste synthetic resin is successively fed into the vessel by the screw conveyor. The heating vessel is heated by a heater. The heating vessel is adapted to heat the waste synthetic resin fed thereinto, thereby melting and gasifying the resin. The gaseous synthetic resin is transferred into a condenser. In the condenser, the gasious synthetic resin is cooled and thereby converted into liquid oil.
In the apparatus having a screw conveyor, a heater is provided on the outer circumferential surface of the screw conveyor. The outer circumferential surface is heated by the heater. Waste synthetic resin is transferred by the heated screw conveyor and melted and gasified during the transfer. The gas is transferred through a gas pipe into a condenser. In the condenser, the gas is cooled and liquified to become oil.
Further, apparatus for converting waste synthetic resin into oil is disclosed in Published Unexamined Japanese Patent Application No. 22776/1976 and Japanese Patent Publication No. 1949/1977. This apparatus is provided with a melting tank in which the synthetic resin is melted and a reaction tank in which the synthetic resin is gasified. No. 48086/1985, an apparatus for converting synthetic resin into oil is disclosed in which a heating vessel used for heating and thermally decomposing the synthetic resin is uniformly heated. In this apparatus, the heating vessel is disposed in a heating furnace. The space between the heating furnace and the heating vessel is filled with a heat transmission medium so as to uniformly heat the heating vessel. As the heat transmission medium, sand, potassium, nitrate, sodium nitrate or the like is used. In this apparatus, the heating vessel is heated through the heat transmission medium and therefore it can be uniformly heated.
An apparatus for converting synthetic resin into oil using a heating furnace is advantageous in that the produced oil can be used as a fuel for melting and gasifying the synthetic resin. Accordingly, this apparatus is advantageous in that no extra fuel is consumed. The amount of the oil consumed in melting and gasifying the waste synthetic resin is about 10% to 20% of the oil produced from the waste synthetic resin.
However, the method of coverting synthetic resin comprising heating the heating vessel by a heating furnace is disadvantageous in that the amount of residuary substances not converted into oil and left in the heating vessel is large, and that the amount of gaseous components is large with a low yield of oil.
It is very important for such an apparatus to reduce the amount of residuary substances left in the heating vessel and to increase the yield of oil. It is laborious to take out a large amount of residuary substances and it is also laborious and expensive to dispose of them. Further, since the yield of oil is small, the waste synthetic resin cannot be effectively recycled.
In an apparatus for converting synthetic resin into oil in which the heating vessel is heated by a heating furnace, a large amount of residuary substances are left in the heating vessel and the yield of oil is low because it is difficult to control the temperature distribution in the heating vessel to the optimum condition.
In an apparatus in which the heating vessel is disposed in the heating furnace, when the heating vessel is heated by a burner, the synthetic resin in the vessel is melted and gasified in the following manner.
1. The synthetic resin fed into the heating vessel settles at the bottom of the vessel.
2. The heating vessel is heated from the bottom thereof by a burner.
3. The heated synthetic resin is melted at the bottom of the heating vessel. Therefore, molten synthetic resin settles at the bottom of the heating vessel.
4. The molten synthetic resin is further heated and gasified. The upper part of the heating vessel is full of gaseous synthetic resin.
5. The molten synthetic resin settles at the bottom of the heating vessel. Therefore, the temperature rise in the bottom part of the heating vessel is limited by the evaporation heat. Usually, the temperature of the molten synthetic resin is about 350.degree. C. to 450.degree. C.
6. The upper part of the heating vessel full of gas is heated to a high temperature. This is because the upper part cannot be maintained at a fixed temperature owing to the presence of molten synthetic resin.
7. The gas in the heating vessel is heated by the heating vessel heated to a high temperature.
8. The gas heated to a high temperature produces carbon and the carbon is deposited on the inner surface of the heating vessel. Further, the gas is thermally decomposed to produce a large amount of low distillate gas components.
Accordingly, an apparatus for converting synthetic resin into oil in which the heating vessel is heated by a heating furnace is disadvantageous in that a large amount of residuary substances is left in the vessel and the yield of oil is low. In an apparatus for converting synthetic resin into oil in which the space between the heating vessel and the heating furnace is filled with heat transmission medium, the heating vessel can be uniformly heated. However, since the heating vessel is heated through the heat transmission medium by the heat in the furnace, the thermal efficiency as a whole is low and a large amount of oil is consumed as fuel. Further, such an apparatus is disadvantageous in that although the heat transmission medium is required to be sufficiently circulated by convection so as to uniformly heat the vessel through the heat transmission medium, such convection of the heat transmission medium is hard to achieve.